A number of electronic ignition systems have been developed to provide spark ignition for multi-cylinder internal combustion engines. Among them capacitor discharge systems, in which a capacitor or group of capacitors, is charged to a relatively high voltage and then rapidly discharged by controlled rectifiers through ignition transformers to fire the spark plugs of the various cylinders, have proven highly satisfactory. In many such systems it is desirable, for reasons of cost and size, to provide a single power source, such as a set of alternator stator windings, to charge the capacitor or capacitors. In such an arrangement, however, should one of the highly stressed controlled rectifiers or one of the capacitors for one cylinder short circuit, the entire system will generally cease functioning, since the shorted circuit element will usually draw substantially the full output of the power supply.